·Since a major part of the tumor is hypoxic,
reductions in size after a fraction of Radiotherapy reoxygenates previously
hypoxic cells, making them radiosensitive.

•Reassortment

·Dividing cells are sensitive to RT in specific
phases of the cell cycle

·As tumor cells are in different phases of the
cell cycle, those in radiosensitive phase get killed first. Remaining cells
continue the cycle and are killed at the next fraction of RT when they reach
Radiosensitive phase.

1.Adjuvant RT: Application
of RT after any kind of treatment modality. If given immediately after
surgery, post-op RT

2.Neo-Adjuvant RT: Application
of RT before any kind of treatment modality. If given immediately before
surgery, pre-op RT

3.RadioChemotherapy syn. Concurrent
ChemoRadiotherapy (CCRT): Application of RT concurrently with
Chemotherapy. Can be Adjuvant or Neo-Adjuvant.

•According to MODE of delivery of
Radiotherapy

•External Beam RadioTherapy: Given
externally to the patient by a treatment machine e.g. Linear Accelerator

•Brachytherapy: Given
by implanting Radioactive sources directly on patient (Interstitial) or
in body cavities (Intracavitary).

•Intra-Operative RadioTherapy: Given
directly to Tumor Bed at time of surgery.

•Stereotactic Radiotherapy/RadioSurgery: Given
externally by utilizing a rigid frame to deliver high doses in few fractions,
to critical sites (e.g. CNS tumors) using a special machine. e.g. Gammaknife

•Intensity Modulated Radiotherapy (IMRT): A
Highly developed form of 3DCRT, in which the radiation dose is tightly
conformed around tumor. Spares most normal tissue.

•Image Guided Radiotherapy (IGRT): IMRT
delivered in conjunction with a daily CT scan of patient done by the treatment
machine. Used to account for changes in size of tumor and accurately adjust for
variations in normal tissues.